DESCRIPTION: (provided by the applicant): The long term objective of this project is to understand the unique role of the mitochondrial ATP synthase in the life cycle of the parasitic protozoan, Trypanosoma brucei. This critically important enzyme complex couples the proton motive force generated by the electron transport chain to the synthesis of ATP. It is also capable of utilizing ATP generated by substrate level phosphorylation to generate a proton motive force in the absence of a functional electron transport chain. We have shown that this key enzyme is regulated by multiple mechanisms throughout the T. brucei life cycle but, unlike the cytochromes, is still expressed in all of the bloodstream forms. The goals of this proposal are to determine whether the ATP synthase is required throughout the life cycle of T. brucei and to determine the vital steps in this enzyme's synthesis - The questions that the specific aims of this grant address are 1. What is the complete structure of the mitochondrial ATP synthase in T. brucei ? 2. Is there a common regulatory mechanism for the expression of the nuclearly encoded genes of the T. brucel mitochondrial AlP synthase? 3. What is the effect of decreasing the level of the mitochondrial ATP synthase in bloodstream forms? 4. Can a partial mitochondrial ATP synthase assemble without the mitchondrially encoded subunits and does it have enzymatic function? The results from these experiments will provide us with an understanding of the interplay between nuclear and mitochondrial genes required to produce mitochondrial complexes and will provide insight into the significance of the ATP synthase in all life cycle stages of T. brucei. The information gained may provide a mechanism to specifically target this key bioenergetic enzyme complex using a chemotherapeutic approach.